Determination of the elongational viscosity of polymer melts by melt spinning experiments. A comparison with different experimental techniques

In this work, melt spinning experiments were tentatively used for the determination of the elongational viscosity of polymer melts at different levels of tensile strain and strain rate. The materials examined were two high-density polyethylene grades for blow moulding with similar number-average molecular mass but different polydispersity index. The data from melt spinning tests were compared with transient extensional viscosity data obtained by uniform isothermal tensile tests, performed by means of an extensional rheometer, as well as with those produced by converging flow tests (Cogswell model). The results showed that for high strain and strain rate levels, the melt spinning experiments provide elongational viscosity data quite close to the transient extensional viscosity values obtained from the tensile tests.     

Necking in non-isothermal high-speed spinning as a problem of sensitivity to external disturbances

Necking in non-isothermal high-speed melt spinning is treated as a problem of sensitivity to external disturbances at both ends of the spin-line. Necessary conditions for existence of necking are formulated in terms of the corresponding increments of velocities, forces, viscosities, etc. It is shown that necking may be present in the high-inertia range for a rather small viscosity variation. Small inertia effects require higher values of the radial viscosity gradients.     

旋涂速度对制备P3HT有机场效应晶体管性能的影响

采用溶液化的方法制备了以PMMA为绝缘层、P3HT为有源层的有机场效应晶体管.研究了P3HT有源层和PMMA绝缘层的旋涂速度对器件性能的影响.实验结果表明,当P3HT和PMMA的旋涂速度均为2 000 r/min时,器件的性能最佳.峰值场效应迁移率为6.84×10^-2 cm²·V^－1·s^－1.结果表明,选择适当的旋涂速度是一种有效提高溶液化制备有机场效应晶体管性能的方法.     

Solid-state NMR detection of 14N-13C dipolar couplings between amino acid side groups provides constraints on amyloid fibril architecture

Solid‐state nuclear magnetic resonance (SSNMR) is a powerful technique for the structural analysis of amyloid fibrils. With suitable isotope labelling patterns, SSNMR can provide constraints on the secondary structure, alignment and registration of β‐strands within amyloid fibrils and identify the tertiary and quaternary contacts defining the packing of the β‐sheet layers. Detection of ¹⁴N? ¹³C dipolar couplings may provide potentially useful additional structural constraints on β‐sheet packing within amyloid fibrils but has not until now been exploited for this purpose. Here a frequency‐selective, transfer of population in double resonance SSNMR experiment is used to detect a weak ¹⁴N? ¹³C dipolar coupling in amyloid‐like fibrils of the peptide H₂N‐SNNFGAILSS‐COOH, which was uniformly ¹³C and ¹⁵N labelled across the four C‐terminal amino acids. The ¹⁴N? ¹³C interatomic distance between leucine and asparagine side groups is constrained between 2.4 and 3.8 Å, which allows current structural models of the β‐spine arrangement within the fibrils to be refined. This procedure could be useful for the general structural analysis of other proteins in condensed phases and environments, such as biological membranes. Copyright © 2011 John Wiley & Sons, Ltd.     

Numerical simulation of a two-phase melt spinning model

We consider a two-phase model of melt spinning including flow induced crystallization. Introducing slight modifications in the model we perform numerical simulations on it. We present comparison of our velocity profiles with the experimental profiles provided by the company Freudenberg & Co.     

Melt Electrospinning

Melt electrospinning is relatively under‐investigated compared to solution electrospinning but provides opportunities in numerous areas, in which solvent accumulation or toxicity are a concern. These applications are diverse, and provide a broad set of challenges to researchers involved in electrospinning. In this context, melt electrospinning provides an alternative approach that bypasses some challenges to solution electronspinning, while bringing new issues to the forefront, such as the thermal stability of polymers. This Focus Review describes the literature on melt electrospinning, as well as highlighting areas where both melt and solution are combined, and potentially merge together in the future.     

聚乳酸/二氧化硅静电纺丝复合纤维膜的制备与表征

为提高聚乳酸（PLA）静电纺丝纤维膜的热性能及机械性能,以PLA为基体,正硅酸乙酯为SiO₂前驱体,通过溶胶-凝胶法和静电纺丝工艺制备PLA/SiO₂复合纤维膜。研究表明：通过静电纺丝,SiO₂被成功引入PLA基体制备成纤维膜,其中PLA呈非晶态,且SiO₂增大了PLA的分子间距;SiO₂的引入可以显著提高800 ℃时的残余量;SiO₂可以提高复合纤维膜的断裂强度和断裂伸长率,且当（SiO₂）为1 %时,断裂强度和断裂伸长率分别提高至2.82 MPa和42.2 %;静电纺丝纤维膜内的纤维无序排列,粗细不均匀,SiO₂引入后,PLA的孔洞更加明显、致密。总之,SiO₂引入PLA基体后,复合纤维膜在800 ℃的残余率显著提高,断裂强度及断裂伸长率改善,且形成致密的孔洞结构。     

Fabrication of continuous fiber-reinforced thermoplastic composites with structural gradient from sheath-core type bicomponent fibers

Sheath-core type bicomponent fibers of polypropylene (PP) as a sheath component and thermotropic liquid crystalline polymer (TLCP) as a core component were prepared by the highspeed melt spinning process. Continuous fiber reinforced thermoplastic composites, in which TLCP acts as a reinforcing fiber and PP as a matrix polymer, were fabricated by the compression molding of these fibers. In the melt spinning, the attainable highest take-up velocity of TLCP was improved by co-processing with PP. Tensile modulus and strength of the TLCP component in the PP/TLCP bicomponent fibers increased with an increase in the take-up velocity. Comparison of wide-angle X-ray diffraction patterns of starting bicomponent fibers and fabricated composites indicated that the orientation relaxation of TLCP did not occur in the compression molding process. Accordingly, the tensile modulus and strength of the PP/TLCP composites were similar to those of the bicomponent fibers. Continuous fiber reinforced thermoplastic composites with various types of fiber content distributions were fabricated from the bicomponent fibers in which sheath-core composition was changed gradually in the spinning process. In the three-point bending test, the composites with two different types of symmetric structural gradients, one with higher TLCP fiber content near the surfaces than in the center and the other with higher TLCP content in the center than near the surfaces, exhibited different flexural moduli even though the overall TLCP contents were comparable. In the three-point bending test of a composite with asymmetric structural gradient, the yielding behavior and maximum flexural load varied depending on the direction of load application although the initial flexural moduli were similar.     

固体高分辨~(13)C NMR研究γ线辐照对结晶聚乙稀聚集态结构的影响

结晶聚乙烯(PE)经~(60)Coγ线辐照后,用固体高分辨~(13)C NMR CP/DD/MAS方法观测解析了辐射效果与具有片晶结构的结晶相,结晶—橡胶状无定形界面相以及橡胶状无定形相的聚集态结构的关系。考察了各相中的~(13)C核自旋—晶格弛豫和自旋-自旋弛豫行为及辐照对其影响。得到辐照后产生交联,破坏,相转变及晶型变化等有意义的结果,对PE的辐照效应和机制的探讨提供了核磁共振的新实验证据。     

转杯纺半自动接头质量提高的研究

通过对转杯纺半自动接头原理和关键技术的阐述，分析其接头质量不理想的原因，进而提出了3种改进措施，包括采用退捻生成纱尾、改变喂给速度和排除损伤纤维。并通过试验验证了前面两者具有较好的效果，特别是改变喂给速度的方法效果更佳。